The present invention relates to a process for manufacturing an adhesive by extrusion, wherein the adhesive comprises at least one degraded polypropylene(co)polymer and at least one additional additive.
The degradation of polypropylene(co)polymers with the help of extruders is well known. By the action of shear forces at high temperature, the molecular weight of polypropylene (co)polymers can be reduced or degraded in a controlled manner due to the resulting thermomechanical stress. A further increase in efficiency of the degradation process is possible when the cited process is carried out in the presence of radical donors, such as for example peroxides.
In this context, DE 4000695 C2, for example, describes a process for manufacturing essentially amorphous poly-alpha-olefins that are manufactured from high molecular weight amorphous poly-alpha-olefins by shear stressing above the softening point in the presence of a radical donor, wherein the melt viscosity of the high molecular weight amorphous poly-alpha-olefin is at least halved. The amorphous poly-alpha-olefins manufactured in this way can be used in heavily loaded coating compounds for carpets or for hot melt adhesives.
Moreover, WO 2001/46277 A2 discloses a process for manufacturing a hot melt adhesive composition that comprises a degraded ethylene propylene copolymer, wherein a starting polymer is degraded by thermomechanical stress in the presence of a radical donor. The degraded ethylene propylene copolymer can be blended before or after its manufacture with further polymers in order to obtain polymer blends.
In conventional processes the addition of further additives to a polymer prior to carrying out the degradation process in an extruder is disadvantageous because in the course of the degradation process a difficultly controllable chemical crosslinking or interaction can occur between polymer and additive. Similarly, the later addition of further additives for manufacturing an adhesive is disadvantageous. This generally requires the already degraded extrusion product to be re-melted, which involves a high consumption of energy and a renewed thermomechanical stress of the degraded polymer, whereby its properties, such as for example its thermal stability under load and/or cohesion can worsen.
Accordingly, the object of the present invention is the provision of an improved process for manufacturing adhesives, such as for example hot melt adhesives.
The present object is achieved by the inventive process for manufacturing an adhesive by means of extrusion.